A pressure tank of this type in the form of a hydraulic accumulator is disclosed in DE 28 52 912 A1. The resilient separating element is formed of a rubber-like material (synthetic rubber, such as acrylic nitrile-butadiene rubber) in the known hydraulic accumulator and forms a membrane movable by deformation and separating the gas side from the liquid side in the accumulator housing. Two main demands must be imposed on the operating behavior of hydraulic accumulators with these membranes movable by deformation. First, the impermeability of the membrane must be ensured to prevent gas diffusion. Second, corresponding mechanical properties of the membrane are necessary, especially ease of movement and high cyclic bending strength to be maintained even under the influence of corrosive media.
In the aforementioned known hydraulic accumulator, these requirements are only partially satisfied. To improve the impermeability of the rubber-like membrane in the known accumulator, annular bead-like elevations project out of the main separating plane in tight succession. Because the elevations increase the average wall density, diffusion tightness is in fact improved. However the significant increase of wall thickness leads to considerable stiffening and accordingly to a deterioration of mobility.